The time-lock is not an old device, but it is already a necessity. Just as the invention of new and impenetrable armor for battle-ships has only produced new cannon or new projectiles which make necessary a still harder protective shell about the ship, so has the increasing ingenuity with which banks guard their treasure been met by a corresponding advance in audacity and skill by those whose trade it is to rob the banks. An old-fashioned safe would be to a bank as useless a toy as one of Gustavus Adolphus’s wooden cannon in a modern fort; and a safe cracker of the past generation would be as helpless as John Bagsbury’s daughter Martha in the presence of a great Harveyized-steel sphere with its electric apron burglar alarm, its half-dozen separate combinations, and its time-lock ticking away inside. The time-lock differs from other devices of the sort in this, that it is no respecter of persons; it makes no discrimination between Trojan and Tyrian, friend and enemy. It resides in a glass-covered box on the inner face of the door. You unlock the cover, turn the knob until the hand upon a dial points to a certain number, and push the door to, and it will not open again until that number of hours has elapsed. It had occurred to Melville Sponley that vaults which could not be unlocked would be as disastrous to a bank as vaults which were empty; and Curtin, carrying out his employer’s instructions that afternoon, after John had gone away, had merely given the little knob in the glass box an extra twist. That was no very difficult thing to do, nor, being done, to make a man afraid. Of course, they would know he had done it. He alone in the bank had the key to the box, save on occasions when he handed it over to Peters. And it was altogether likely that John Bagsbury would suspect him of having done it maliciously. But it would be impossible to prove such a suspicion as that; the excuse was entirely plausible. The bank, on account of the run that day, had closed nearly three hours later than usual, and the assistant cashier, forgetting to take that into account, wound up the spring just as he was in the habit of doing, so that instead of opening at nine, the bolt would not fall out of place until twelve. They could never prove that he meant to do it.